Temporal variability of micro-organic contaminants in lowland chalk catchments: new insights into contaminant sources and hydrological processes

This paper explores the temporal variation of a broad suite of micro organic (MO) compounds within hydrologically linked compartments of a lowland Chalk catchment, the most important drinking water aquifer in the UK. It presents an assessment of results from relatively high frequency monitoring at a well-characterised site, including the type and concentrations of compounds detected and how they change under different hydrological conditions including exceptionally high groundwater levels and river flow conditions during 2014 and subsequent recovery. This study shows for the first time that within the Chalk groundwater there can be a greater diversity of the MOs compared to surface waters. Within the Chalk 26 different compounds were detected over the duration of the study compared to 17 in the surface water. Plasticisers (0.06–39 μg/L) were found to dominate in the Chalk groundwater on 5 visits (38.4%) accounting for 14.5% of detections but contributing highest concentrations whilst other compounds dominated in the surface water. Trichloroethene and atrazine were among the most frequently detected compounds. The limit for the total pesticide concentration detected did not exceed EU/UK prescribed concentration values for drinking water. Emerging organic compounds such as caffeine, which currently do not have water quality limits, were also detected. The low numbers of compounds found within the hyporheic zone highlight the role of this transient interface in the attenuation and breakdown of the MOs, and provision of an important ecosystem service

The baseline concentrations of methane in Great British groundwater : the National Methane Baseline Survey

This report describes the BGS research programme evaluating the baseline concentration of methane in groundwater which ran from November 2011 to completion in March 2016. The aim of the survey has been to improve knowledge of conditions in aquifers overlying potential shale gas source rocks present at depth, thus providing baseline knowledge relevant to the management of future exploration of new hydrocarbon sources. The necessity for doing this has been prompted by evidence from elsewhere (notably the USA) which has revealed very high methane concentrations in groundwater in some areas of shale gas extraction. Although this has often been directly attributed to shale gas operations, there have generally been no pre-development data on methane concentrations available to test this. Before the start of the current survey, BGS held some 170 analyses of methane in groundwaters from aquifers across Great Britain, acquired from the 1980s onwards. These data have been combined with new survey data, to give a total of 439 methane data points. In this combined dataset, 96% of samples show methane concentrations of less than 100µg/l and indicate that methane is rarely present at concentrations high enough to be potentially explosive (there are no health limits for methane in groundwaters). In the minority of samples with elevated concentrations, this was generally considered to be due to the proximity of organic rich coal seams or peats. The highest concentrations were found in the Cretaceous aquifers of the Weald Basin, a known area for occurrences of methane gas in the shallow subsurface. The new survey covers the majority of principal aquifers in Great Britain, including the Chalk, Permo-Triassic Sandstones, Carboniferous Limestone, and the Lower Greensand. Samples from over twenty different aquifers have been collected. In general, methane concentrations in carbonate aquifers (Chalk, limestones, Oolites etc.) are low, similar to those seen in the Permo-Triassic sandstone aquifers, although methane is widely present above detection limit (approximately 1µg/L) in all these aquifers. The Coal Measures of South Wales have the highest median value across Great Britain and this aquifer also shows the greatest temporal variability. Methane concentrations in the Carboniferous sediments of Scotland are also elevated, likely due to the impact of mining and the presence of coal seams. While little temporal variability is generally seen in aquifers used for public water supply or otherwise regularly pumped, further work is required to understand the impact of borehole use, pumping regime and aquifer type on the variability of the methane baseline of Great British aquifers. It should be noted that the Survey is not intended to replace any oil and gas operator’s local monitoring as required by the regulators. This is a national scale survey to enable a broad understanding of the distribution of methane in aquifers across relevant areas of Britain and cannot replace an understanding of groundwater quality at a local scale

Persistent and emerging micro-organic contaminants in Chalk groundwater of England and France

The Chalk aquifer of Northern Europe is an internationally important source of drinking water and sustains baseflow for surface water ecosystems. The areal distribution of microorganic (MO) contaminants, particularly non-regulated emerging MOs, in this aquifer is poorly understood. This study presents results from a reconnaissance survey of MOs in Chalk groundwater, including pharmaceuticals, personal care products and pesticides and their transformation products, conducted across the major Chalk aquifers of England and France. Data from a total of 345 sites collected during 2011 were included in this study to provide a representative baseline assessment of MO occurrence in groundwater. A suite of 42 MOs were analysed for at each site including industrial compounds (n = 16), pesticides (n = 14) and pharmaceuticals, personal care and lifestyle products (n = 12). Occurrence data is evaluated in relation to land use, aquifer exposure, well depth and depth to groundwater to provide an understanding of vulnerable groundwater settings

A baseline survey of dissolved methane in aquifers in Great Britain

Interest in dissolved methane (CH4) concentrations in aquifers in England, Scotland and Wales (‘Great Britain’ or GB) has grown concurrently with interest in the exploitation of unconventional gas sources (UGS). Experience, mainly from North America, has shown the importance of a pre-production baseline against which changes possibly due to UGS extraction can be compared. The British Geological Survey, aided by water utilities, private users and regulators, has compiled a unique dataset for CH4 in groundwaters of GB. This focuses principally on areas where UGS exploration is considered more likely, as indicated by the underlying geology. All the main water supply aquifers (Principal aquifers) were targeted, plus Secondary aquifers where locally important. The average dissolved CH4 concentration across GB in the aquifers sampled was 45 μg/l. Out of a total of 343 sites, 96% showed dissolved CH4 concentrations b100 μg/l, 80% b10 μg/l, and 43% b 1 μg/l. No site had a CH4 concentration above the US Department of the Interior suggested risk action level of 10,000 μg/l. While most sites were sampled only once, a sub set was monitored quarterly to determine the magnitude of seasonal or other variations. Generally these variations were minor, with 84% of sites showing variations within the range 0.5–37 μg/l, but some aquifers where the porosity was primarily fracture-related showed larger changes (0.5–264 μg/l). This may have been due to the nature of sampling at these sites which, unlike the others, did not have installed pumps. Since the regulatory compliance monitoring attending UGS operations will include the measurement of parameters such as dissolved CH4, it is essential that sampling methods are tested to ensure that reliable and comparable datasets can be obtained

Emerging contaminants in groundwater

The term ‘emerging contaminants’ is generally used to refer to compounds previously not considered or known to be significant to groundwater (in terms of distribution and/or concentration) which are now being more widely detected. As analytical techniques improve, previously undetected organic micropollutants are being observed in the aqueous environment. Many emerging contaminants remain unregulated, but the number of regulated contaminants will continue to grow slowly over the next several decades. There is a wide variety of sources and pathways for these compounds to enter the environment and these include agriculture and urban areas. Some of these contaminants can have human or ecological health effects and there is a need for better understanding of their fate in environmental systems. This report provides a short review of the types of organic micropollutants which can be found in the aqueous environment. These include nanomaterials, pesticides, pharmaceuticals, industrial additives and by-products, personal care products and fragrances, water treatment by-products, flame/fire retardants and surfactants, as well as caffeine and nicotine metabolites and hormones. Many of the compounds are relatively small polar molecules which are not effectively removed by conventional drinking water treatment using activated carbon. Pesticides and some industrial compounds are presently covered by the Water Framework Directive, the Groundwater Regulations and the Drinking Water Directive. Additional parameters, such as bisphenol A and nonyl-phenol are anticipated to be covered by revisions to the Drinking Water Directive. Others are currently unregulated. In order to assess the hazards presented by such compounds, information on usage, persistence, leachability and a robust sensitive analytical method is required. The UK metaldehyde problem was not originally discovered due to lack of an analytical method and was exacerbated by recalcitrance in water treatment. For many pesticides these requirements are fulfilled and an assessment of risk of leaching to groundwater can be made. However, for pesticide metabolites this information can be sparse and for compounds such as pharmaceuticals it can be lacking. A simple hazard assessment for currently approved pesticides was made from information on UK usage, persistence, sorption to soil carbon and published leaching indices. The following compounds were assessed as having the greatest potential for leaching to water: 2,4-D, amidosulfuron, bentazone, clopyralid, dicamba, florasulam, fosthiazate, imazaquin, iodosulfuron-methyl-sodium, maleic hydrazide, MCPA, MCPP-P, metribuzin, metsulfuronmethyl, quinmerac, oxamyl, and triclopyr with a further 46 also having potential. Of these, 19 had an octanol/water partition coefficient (Kow) less than that of metaldehyde and therefore are likely to be incompletely removed by water treatment. A simple assessment for pesticide metabolites, based only on organic carbon/water partition coefficient (Koc) and persistence data, in this study gave results which agreed in principle with other studies. The different approaches indicate that the metabolites of chlorothalonil, cyanazine, diflufenican, flufenacet, iodosulfuron-methyl, metaldehyde, metazachlor and metsulfuron-methyl are likely to pose the greatest risk to drinking water. In many cases these metabolites are derived from parents which have a lesser risk. Other organic micropollutants, such as pharmaceuticals, cannot as yet be assessed in the same way due to a lack of persistence data since the majority of persistence studies have been directed at water treatment. A range of organic micropollutants from urban settings have been detected in ground and surface water. Commonly detected compounds include: bisphenol A, carbamazepine, galaxolide, ibuprofen, iopamidol, phthalates, phenyl ethoxylates, and sulfamethoxazole. Case studies show that a small number of contaminants may be used to characterise the contaminant loading and also be used to assess the migration pathways in urban areas. Data interpreted by BGS from the Environment Agency’s monitoring programme for organic pollutants indicates that the 30 most frequently detected compounds comprise both established and emerging compounds and include a number of polyaromatic hydrocarbons, petroleum compounds, triazine herbicides, chlorinated solvents, degradation products and THMs, caffeine, DEET and industrial compounds such as bisphenol A and tributyl phosphate. Specific determinands include a range of currently licensed and phased out pesticides with a few metabolites, pharmaceuticals including carbamazepine and triclosan, caffeine, nicotine and food additives and alkyl phosphates. These data exhibit hot spots which may indicate possible research areas. Future research should focus on a compound identified in the literature and detected by Environment Agency monitoring. Possible topics could be a study of migration through the unsaturated zone. In many cases the mechanism for migration of emerging contaminants from the surface to groundwater is very unclear